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<title>GRASS -- GRASS Rasters</title>
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<h1>GRASS -- GRASS Rasters</h1>

GDAL optionally supports reading of existing GRASS raster layers (cells, and
image groups), but not writing or export.  The support for GRASS raster 
layers is determined when the library is configured, and requires libgrass
to be pre-installed (see Notes below). <p>

GRASS rasters can be selected in several ways.<p>

<ol>
<li> The full path to the cellhd file for the cell can be specified.  This
is not a relative path, or at least it must contain all the path components
within the database including the database root itself.  The following
example opens the cell "proj_tm" within the mapset "PERMANENT" of the
location "proj_tm" in the grass database located at /u/data/grassdb.<p>
eg.<br>
<pre>
  % gdalinfo /u/data/grassdb/proj_tm/PERMANENT/cellhd/proj_tm
</pre>
<li> The full path to the directory containing information about an imagery
group (or the REF file within it) can be specified to refer to the whole
group as a single dataset.  The following examples do the same thing.<p>
eg.<br>
<pre>
  % gdalinfo /usr2/data/grassdb/imagery/raw/group/testmff/REF
  % gdalinfo /usr2/data/grassdb/imagery/raw/group/testmff
</pre>
<li>  If there is a correct .grassrc5
setup in the users home directory then cells or imagery groups may be opened 
just by the cell name.  This only works for cells or images in the current 
location and mapset as defined in the .grassrc5 file. <p>
</ol>




The following features are supported by the GDAL/GRASS link.<p>

<ul>
<li> Up to 256 entries from cell colormaps are read (0-255).  
<li> Compressed and uncompressed integer, floating point and double precision
cells are all supported.  Integer cells are classified with a band type of
"Byte" if the 1-byte per pixel format is used, or UInt16 if the two byte
per pixel format is used.  Otherwise integer cells are treated as UInt32.
<li> Georeferencing information is properly read from GRASS.
<li> An attempt is made to translate coordinate systems, but some conversions
may be flawed, in particular in handling of datums and units.
</ul>

See Also:<p>

<ul>
<li> <a href="http://grass.itc.it/">GRASS GIS Home Page</a>
<li> <a href="http://home.gdal.org/projects/grass/">libgrass page</a>
</ul>

<hr>
<h2>NOTES on driver variations</h2>

For GRASS 5.7 Radim Blazek has moved the driver to using the GRASS
shared libraries directly instead of using libgrass.  Currently (GDAL 1.2.2 and later)
both version of the driver are available and can be configured using
"--with-libgrass" for the libgrass variant or "--with-grass=&lt;dir&gt;" for the 
new GRASS 5.7 library based version.  The GRASS 5.7 driver version is currently
not supporting coordinate system access, though it is hoped that will be
corrected at some point.<p>

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